1. Field of the Invention
This invention relates to a method and apparatus for separating a brittle material, and more particularly, a method for both scoring and separating a glass substrate using only a single beam of radiation.
2. Technical Background
Sheets of glass are conventionally cut or separated by mechanical means, whereby the glass is scored along a predetermined path, and a mechanical bending force thereafter applied to one or both portion of the sheet to separate the sheet. During the scoring step, a median (vent) crack is formed which travels only a portion of the way through the thickness of the sheet.
In another conventional method, an initial flaw is placed in the sheet. A laser is then directed at the flaw, thereby heating the glass and extending the flaw along a predetermined path. U.S. Pat. No. 5,692,284 to Kondratenko describes a process wherein the beam spot has a short elliptical shape with the longest axis of the spot less than 20 mm. The reported scoring speed was low, and varied in the range between about 10-120 mm/sec, depending upon the glass type. U.S. Pat. No. 5,776,220 to Allaire, et al. teaches a significantly longer elliptical spot, with the longest axis greater than 40 mm. U.S. Pat. No. 6,211,488 to Hoekstra, et al. discloses using a plurality of laser beams preceding the scoring beam to increase the scoring speed. A similar approach based on using several beams to increase the scoring speed is taught in U.S. Pat. No. 6,800,831.
The separating step involved deepening the vent crack, either through a bending moment applied to the vent crack as described above, or by heating the score line with a laser to create tensile stress. For example, U.S. Pat. No. 6,541,730 describes using a second laser beam of circular or elliptical shape traveling behind the scoring beam.
The preceding techniques generally involve several steps and or laser beams to accomplish both the scoring and the separating functions. Such multiple step, multiple beam methods add cost, and complicate the optical implementation of the scoring and separating process. What is needed is a non-contact method of scoring and separating a brittle material (e.g. a glass substrate) in a single step, without the added complication of multiple beams from a plurality of radiation sources.